The present invention relates generally to variable pitch radiator fans, and in particular to a control system for a variable pitch radiator fan.
Variable pitch radiator fans for use in motor vehicles have been proposed. U.S. Pat. No. 6,729,844 to Bettencourt and assigned to the inventor, is directed to a control system for a cooling fan with variable pitch blades. Electronic control device 10 operates variable pitch fan assembly 12. The '844 patent discloses a system and method for controlling variable pitch fan assembly 12 based on three parameters: (1) a temperature parameter, (2) a pressure parameter, and (3) a timing device. A switch is associated with each of these three parameters, and based in the position of the various switches, the pitch of the fan blades is adjusted.
The temperature parameter is coupled to the engine block. But Bettencourt also teaches other locations, such as an oil cooler, the engine radiator 24, a heat exchanger, an air conditioner condenser 104 or the air charge cooler 106. See column 7, lines 20-25. The pressure parameter is related to a change in pressure of the air conditioning system as measured by an air conditioner pressure switch. See column 6, lines 32-34, and column 7, lines 42-44. Bettencourt also discloses the use of a timer. The timer is used to change the blade pitch at predetermined intervals of time. See column 11, line 11 to column 12, line 41. In the example given in that portion of the specification, the timer is used to place the blades in the full neutral position (no airflow) for 20 minutes after the engine is started, and then after 20 minutes, enter a full purge mode (full reverse or push mode) for 8 seconds, and then return to the neutral position.
A system of relays, switches and solenoids are used to define the operating logic of the system. A summary of the operating logic is shown in FIG. 6. Basically, if the timer relay is closed, the blade pitch is set to full reverse. If the timer relay is open (not operating) the temperature and pressure switches govern the fan blade pitch position.
U.S. Pat. No. 6,659,894 to Kern and assigned to Generac Power Systems Inc., is directed to a variable pitch sheave assembly. The variable pitch sheave assembly is used to control the speed of a fan that is used to cool an engine driven electrical generator. In Kern, the term “variable pitch” is not used to describe the pitch of the propeller blades of the fan, but rather the pitch or spacing of a sheave pulley assembly. This sheave pulley system is shown in FIGS. 12 and 13. The variable pitch sheave assembly operates in a manner that is similar to most continuously variable transmissions (CVT). The sheaves move axially along a rod and their motion varies the gear ratio between two drive pulleys. By changing the gear ratio, current changes the fan speed. It is important to note that Kern does not change the pitch of the propeller blades. The Kern device is also not responsive to engine speed, water temperature, or intake air temperature.
U.S. Pat. No. 6,644,922 to McCallum et al. and assigned to Flexxaire Manufacturing, Inc., is directed to a variable pitch fan. The fan disclosed in McCallum can be used in combination with earth moving equipment including engines made by Caterpillar, Inc. See column 1, lines 16 and 17. McCallum teaches blades 14 of cooling fan 10 that have a plurality of blade positions, including a push position (reverse blade position), a pull position (conventional or normal position) where air is blown from the front of the vehicle towards the engine, and a neutral position in which the rotation of the blades continues but blocks air flow. The blades of McCallum's variable pitch fan can be adjusted in small increments from reverse to normal pitch position. McCallum also teaches the concept of sensing a number of variables to control or set the pitch of the blades. McCallum teaches sensing the following variables: conventional speed or RPM (revolutions per minute), engine coolant temperature, intake air temperature, hydraulic oil pressure, transmission oil temperature, brake coolant temperature, pressure or air conditioner condenser temperature, or any other sensor that indicates a cooling load.
McCallum, however, does not teach or render obvious the concept of changing the pitch of a fan in response to vehicle speed or motion including idle, forward motion or reverse motion. McCallum also does not teach the concept of using an independent fan speed. In McCallum, the fan is directly coupled to the engine and the fan speed is proportional to engine speed. See column 12, lines 61-67.
U.S. Pat. No. 6,253,716 to Palmer et al. and assigned to Horton, Inc., is directed to a control system for a cooling fan with variable pitch blades. The control system of Palmer is responsive to one or more operational parameters and a second signal related to a cooling requirement.
Palmer discloses several different embodiments. In one embodiment, the operational parameter is engine speed, and the cooling requirement is provided by Electronic Control Module (ECM) 205. The ECM includes a signal generator 225, and this signal generator provides a pulse width modulated signal to CPU 200. ECM 205 provides a cooling level, one example of which is a cooling level of 50%. See column 7, lines 44 to 58. In this first embodiment, CPU 200 uses the engine speed and the desired cooling level provided by ECM 205 to compute the blade angle. In a second embodiment, charge air intercooler temperature and engine coolant temperature are monitored, and the blade pitch is set based on these two conditions.
U.S. Pat. No. 6,564,899 to Na and assigned to Samsung Heavy Industry Co., Ltd., is directed to a control system for a cooling fan with variable pitch blades. Controller 30 is electrically connected to a sensor 20 disposed in a water conduit 13 that connects from the engine to radiator 8. A signal from sensor 20 is used to calculate the blade angle.
While the related art teaches various blade pitch control systems, the related art fails to teach a blade pitch control system that is responsive to a number of environmental or operating conditions including vehicle speed. The related art also fails to teach a control system capable of independently controlling two or more radiator fans. Finally, the related art fails to teach the concept of providing a circulation effect or mode where the blade pitch of two fans is opposed.